There have been numerous news announcements, mostly from NASA's Kepler planet hunting observatory, about the discovery of so-called "Earth-like" worlds nestled inside a star's habitable zone.
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Kepler reports on a planet's orbit size, radius, and apparent size. We know next to nothing about the physical characteristics of these worlds including tectonic and magnetic activity, atmosphere composition, axial tilt, and other conditions affecting climate.
But two reliable metrics are pinpointing the location of the planet in the star's habitable zone and the star's age. Unfortunately, stellar ages are not that well know for candidate habitable planets.
Based on their assessment, the researchers say that the planet Gliese 581g is the "most habitable exoplanet found to date." It's located smack dab in the middle of a red dwarf's habitable zone. the world's temperatures will be moderate for another 5 billion years longer than the span of Earth's habitability window.
The planet may be as small as Earth and therefore have similar gravity, and surface topography. At only 20 light-years away it would be a logical destination for the first interstellar reconnaissance probes. So far, the planet has been the target of (unsuccessful) SETI searches.